This invention relates to yarn winding and, more particularly, to methods and apparatus for doffing and donning yarn packages on a metier.
In accordance with conventional practice, synthetic yarns, such as cellulose acetate, are extruded through dies and pass downwardly through a drying cabinet assembly as continuous filaments. The ends emerge from the drying cabinet assembly at the winding stations which are spaced at uniform intervals along the length of the metier. One type of metier that has been in use for many years has a rotary shaft that extends along the length of the metier. Feed rolls are fixed on the shaft at each winding station. The shaft turns continuously and the ends are wrapped on the feed roll, which maintains a substantially constant tension in the yarn ends. At each winding station, a rotary cam is positioned above the feed roll for winding two of the ends on tubular packages which are mounted on a mandrel or the upper package spindle. Another rotary cam is mounted below the feed roll for winding the other two yard ends on packages mounted on the lower package spindle. Both of the cams rotate continuously and each cam has a pair of spiral grooves which cause the yarn to traverse across the package during a winding operation. As the yarn builds on the bobbins, the spindles move progressively away from the cam, although the surface of the package remains in driving engagement with the cam.
Typically, many winding stations are provided on each metier and operators are employed to doff the filled packages periodically and to donn the take-up tubes or packages on the mandrels. In order to accomplish this, the operator must sever the yarn ends between the cam and the feed roll, remove the yarn package, replace the yarn package with an empty take-up package and throw on the yarn ends. During this process, the ends that have been severed accumulate on the feed roll and after making the throw on, the operator removes the waste yarn. It may take the operator as long as one to two hours, or more, to complete the doffing of an entire metier, depending upon the denier of the yarn and the size of the yarn packages, and the number of yarn ends being extruded on the metier.
In a plant that has many metiers, it is necessary to maintain a schedule for the operators to make maximum use of their time. Significant savings in labor costs could be realized if the time required for making the doff could be significantly reduced. This would provide greater flexibility in scheduling the individual operators. Furthermore, automation of the doffing operation would permit the use of less skilled labor, without reducing the percentage of successful doffs.
Previous attempts to design equipment for automatically doffing metiers typically are prohibitively expensive. A factor in contributing to the high cost of this prior equipment is the means for positioning accurately the apparatus relative to each winding station. Alignment of the apparatus is necessary to provide the proper interaction between the components on the metier and the components on the doffing apparatus. Another handicap in designing doffing apparatus is the presence of a potentially explosive atmosphere around the metiers, which prohibits the use of electrical equipment in which sparking may occur. Thus, for protection against this hazard, electrical equipment should not be used.